Various optical scanning apparatuses have been developed to read and decode optical indicia, such as bar code symbols on a target such as a label. While early bar code scanners were designed to read symbols at a relatively close distance, there exists a need to read symbols at greater and greater distances, for example in warehousing environments. Conventional optical scanning systems, such as hand-held bar code laser scanners, typically have a limited working range due to the constraints imposed on the optical assembly. Motorized systems with additional lenses or mirrors have been developed to reposition the fixed lens assembly along the optical path, thereby moving the laser beam waist and increasing the working range of the scanning apparatus. However, such improvements are complicated and add cost.
For example, U.S. Pat. No. 4,916,318 discloses a polygon mirror mounted to a rotating shaft that deflects a laser beam emitted from a laser source to the target to be scanned. In the scanning apparatus there is a fixed projecting lens disposed between the laser source and the polygon mirror. An optical member, such as a plane parallel plate, is moved in and out of the beam of the laser source to change the beam waist of the laser beam. Several drawbacks to this system exist. The mechanical components required to move the plane parallel plate in and out of the beam are complex, having many moving parts connected by pulleys, belts and the like. Another drawback is that the working range is limited to the thickness of the plane parallel plate. Also, the system is not compact, and is therefore ill-suited for use in a hand-held apparatus.
In another example, U.S. Pat. No. 5,302,812 discloses a scanning apparatus that varies the range of a laser beam waist by moving the fixed convex lens assembly. The fixed lens is moved longitudinally along the optical axis by activation of magnetic coil. The scanning apparatus includes a lens support member supported on a pair of leaf springs so that it can oscillate longitudinally along the optical axis. Permanent magnets are also supported by the leaf springs. Movement of the fixed lens is achieved by varying the strength of the field generated by the magnetic coil. Like the scanning apparatus disclosed in U.S. Pat. No. 4,916,318, this system is complex and adds cost to the scanning apparatus.